3,213,610 United States Patent Office Patented (Oct. 26, 1965 2 about 340 C. On the other hand, thorium, aluminum, 3,213,640 SUBZERO TEMPERATURE FUE AND copper, iron, magnesium and platnium do not ignite in ROCKET GNITION PROCESS these oxidizers even at temperatures ranging at 410° C. John C. Grigger, Oreland, and Henry C. Miller, Hatfield, See, for example, Stein and Vogel, Industrial and En Pa., assignors to Pennsalt Chemicals Corporation, gineering and Chemistry, volume 48, pages 418-21 Philadelphia, Pa., a corporation of Pennsylvania (1956). Therefore, it was surprising to find that niobium No Drawing. Filled Apr. 27, 1962, Ser. No. 190,798 and tantalum of the Group VA metals ignite spontane 12 Claims. (C. 60-35.4) ously at Subzero temperatures in the presence of an oxidizer comprising a halogen fluoride, e.g. chlorine tri This invention relates to methods and means useful O fluoride. It was also surprising to find that tantalum is in rocket propulsion and jet or thrust engines, particularly more reactive than niobium in this respect. at Subzero temperatures. In one of its specific aspects, it The Group VA metals are vanadium, niobium and relates to a hypergolic igniter system. In another of its tantalum. Unlike niobium and tantalum, vanadium does specific aspects, it relates to methods for using said system not ignite spontaneously in a halogen fluoride even at in the ignition of oxidizer-fuel systems in rocket motors 5 room temperature, although vigorous chemical reaction and jet engines. OCCU.S. Hypergolic, or self-igniting, oxidizer-fuel systems are For the practice of the invention, niobium (colum well-known as means for producing gaseous products use bium) and tantalum metal each can be used in commer ful as a source of thrust in rocket motors. A hypergolic cially pure form. Each of these metals also can be used oxidizer-fuel system chemically consists of an oxidizing 20 as an alloy consisting substantially of one of these metals component and a reducing component. The essence of the with the other or with at least one other metal, e.g., iron, mode of operation of a hypergolic system is that the in Zirconium, tungsten or nickel. The metals, or their alloys, dividual chemical components, which alone are not self can be used in the form of pellets, preferably of about igniting in the atmosphere of a combustion chamber, will 0.1 gram in weight or lighter. The metals, or their alloys, ignite spontaneously when brought into intimate contact 25 also can be used in the form of shavings, turnings or fine with each other. The use of such a system, in addition to powder. Also, the metals, or their alloys, can be used in its economic advantages, generally avoids dangers and the form of a suspension within a liquid fuel. They can difficulties resulting from ignition system failures which also be used as an ingredient embedded with a binder in can occur with a system which depends on a non-chemical the surface of and within a solidified form of fuel, for ignition means. 30 example, in an extruded plastic oxidant-fuel composition Practically all hypergolic mixtures have delayed igni containing the niobium or tantalum metal, or an alloy tion periods of Substantially less than one second and thereof, in pellet, shavings, turnings, powdered or other preferably not more than 50 milliseconds at ordinary physical form, alone or in major proportion in combina ambient temperatures at ground level. At lower tem tion with another metal. peratures, this ignition delay period becomes longer. At The oxidizer which is used in practice of the invention Subzero temperatures, i.e., below zero degrees on the cen preferably is halogen fluoride, including chlorine tri tigrade temperature scale, the delay can become danger fluoride, chlorine monofluoride, bromine trifluoride, and ously prolonged and disastrous through build-up of un bromine pentafluoride. The oxidizer can also be halogen ignited combustible materials in a combustion chamber. fluoride in combination with fluorine or with perchloryl Also, in Some cases, complete failure of ignition can re 40 fluoride, or with a mixture of both of the latter materials. sult with materials which become non-hypergolic in the Preferably, the oxidizer is a mixture of halogen fluoride presence of each other due to the low temperature. with perchloryl fluoride. In such a mixture, the ratio of The temperatures commonly encountered in high alti perchloryl fluoride to the halogen fluoride can range from tude operation of aircraft powered by jet or piston en about 24:1 to 1:5 by weight, more perchloryl fluoride gines is in the range of -40° to -57 C. In outer 45 being required to keep the oxidizer in fluid form as the space, it is expected that temperatures of about -100° C. temperature of use is lowered. A mixture of oxidizer are common. At these extremely low subzero tempera containing from about 25% to about 50% by weight of tures, the problems of ignition, or re-ignition after a perchloryl fluoride in the halogen fluoride is preferred. flame-out, of the components even of a system which is Mixtures of perchloryl fluoride with halogen fluoride hypergolic at normal ambient temperatures at ground 50 which are hypergolic to certain fuels at ordinary ambient level become formidable. temperatures are disclosed and claimed in Gall, U.S. We have now found a hypergolic igniter system which Patent 3,066,058. A mixture of halogen fluoride with functions usefully for starting a fire by auto-ignition at fluorine in similar proportions can be used. Also, fluorine a temperature at least as low as that of the freezing point and perchloryl fluoride can be mixed and the mixture of chlorine trifluoride, i.e., at about -83 C., and lower, used with a halogen fluoride, e.g., chlorine trifluoride, in e.g., at about -145 C., in a mixture of halogen fluoride similar proportions as when perchloryl fluoride is used with perchloryl fluoride (ClOF) or fluorine or a mixture alone with the halogen fluoride oxidizer. thereof. We have found that on bringing together sep In practicing the invention in accordance with one em arately and substantially simultaneously an oxidizer com bodiment in Tocket propulsion, chlorine trifluoride and prising a halogen fluoride and a metal fuel comprising 60 tantalum in the form of fine shot are separately and niobium or tantalum, auto-ignition of the resulting mix simultaneously charged into the combustion chamber of ture occurs within a few seconds at about -100° C. and a rocket motor in a way which will be obvious to one in much less than a second at higher temperatures, e.g., skilled in the art such that they immediately come into above around -75° C. intimate contact, thereby spontaneously igniting. For example, the chlorine trifluoride is pumped into the cham It is known in the prior art that certain metals will ber and the shot is blown in with a combustible gaseous ignite at appreciably elevated temperatures, e.g., above material. The gaseous reaction products of combustion about 150 C., in the presence of halogen fluorides. are discharged through the exit orifice of said motor to Thus, uranium will ignite at 150° C., 225 C., 250° C., propel the rocket. and 260 C. in bromine trifluoride, bromine pentafluoride, 70 The halogen fluorides have little or no vapor pressure chlorine trifluoride (CIF) and fluorine, respectively, and at 0° C. Therefore, auxiliary means are usually neces zirconium ignites in chlorine trifluoride or fluorine gas at Sary to charge the halogen fluoride to the combustion 3,218,610 3. 4. chamber. A pump can be used for this purpose if means vention, e.g. chlorine trifluoride containing 50% by for driving the pump are available at the subzero tem weight of perchlory fluoride, and pellets of commer perature. Preferably, however, since pumping means cially pure tantalum of about 0.1' diameter are charged could become inoperative, the halogen fluoride is pres separately and substantially simultaneously into the com surized by means of a gaseous material to a pressure bustion chamber of a rocket motor so that the oxidizer above that of the combustion chamber. An inert gas, envelops the pellets, thereby causing spontaneous igni e.g., nitrogen or helium, can be used for this purpose. tion of the tantalum. Separately and substantially simul However, in some cases it is preferred to use a reactive taneously, a thrust-providing propellant mixture con gaseous material, e.g., perchloryl fluoride or fluorine. sisting of another fuel, e.g., kerosene (JP4), and another Also, since in some cases the temperature of use of the O oxidizer, e.g., oxygen, are charged into the combustion halogen fluoride may be below the freezing point of the chamber. The latter propellant mixture ignites in the halogen fluoride, e.g., below -83 C. in the case of products of combustion of the hypergolic igniter system chlorine trifluoride, an auxiliary liquified gaseous ma of this invention. After the combustion of the thrust terial, such as one of the above group, provides a fluid providing propellant mixture becomes self-sustaining, the medium in which the halogen fluoride can be charged 5 flow of the components of our hypergolic igniter sys into the combustion chamber in the form of a slurry of tem can be discontinued. The gaseous products of reac crystals and thus brought into contact with the metal tion are discharged through the exit orifice of the rocket component of our igniter system, e.g., tantalum in pow motor to propel the rocket. dered form. Despite the fact that the halogen fluoride is In view of the reactivity of niobium and tantalum in crystalline form, when it is brought into contact with 20 metal and their alloys in halogen fluoride, use of these our metal fuel, the reactivity of the metal with the halo metals as materials of construction in the combustion gen fluoride is sufficiently vigorous soon to cause spon chamber must be avoided. However, this fact presents taneous ignition of the metal. On ignition, the auxiliary no great problem because other metals, particularly those material, e.g., perchloryl fluoride, also supports combus forming a protective fluoride film, e.g., Monel or nickel tion of the metal. Therefore, the oxidizer of our inven 25 or 18-8 stainless steel can be used in the combustion tion can be charged to a combustion chamber at ex chamber where the halogen fluoride is present. tremely low subzero temperatures without need for aux The niobium or tantalum metal or one of their alloys iliary mechanical means. can also be dispersed as a stream of fine fluidized powder A metal component of our igniter mixture, e.g., niobi into the path of a liquid or of a powdered solid fuel which um, also can be charged to the combustion chamber with 30 is to be burned in the combustion chamber solely with an out need for auxiliary mechanical means by fluidizing a oxidizer useful in the practice of this invention to pro powder of the metal with a gas, e.g., carbon monoxide, duce the thrust for operation of the rocket motor. The which is non-reactive with the metal in its powdered mixed stream of metal, e.g., niobium, and fuel, e.g., form. Accordingly, by means of our invention, positive powdered coal fluidized with carbon dioxide gas, ignites starting of a fire in the combustion chamber of a rocket 35 spontaneously in a stream of an oxidizer of this inven motor or of a jet engine can be achieved even at extreme tion, e.g., chlorine trifluoride, at a subzero temperature, ly low subzero temperatures without depending on me e.g. in the range of about -1 to -83 C. chanical means for charging the components of the ig Similarly, the mixed stream of our metal fuel and niter mixture to the combustion chamber. another fuel, e.g. unsymmetrical dimethyl hydrazine In another embodiment, the hypergolic igniter system 40 (UDMH) or hydrogen, can be used with an oxidizer of this invention can be used as an igniter system for a comprising halogen fluoride, e.g., chlorine trifluoride, to separate propellant system which is to provide thrust in a provide intermittent bursts of thrust in vector rockets at rocket motor. In such use, an amount of metal from tached to a space vehicle. Thus, positive ignition of the about 0.1 gram to 1.0 gram in wire or particle form is vector rockets at extremely subzero temperatures, e.g., generally adequate to provide sufficient heat and flame 45 -100° C. and lower, is made possible by the practice of on Spontaneous ignition in an oxidizer comprising halo our invention. gen fluoride to ignite the thrust-providing propellant sys The same technique as described in the preceding para tem. The propellant can be in solid form, for exam graph can be employed also in the ignition of jet engine ple, such as that disclosed and claimed in Guth, U.S. motors using JP4 fuel at ordinary ambient temperatures, 2,963,356, but containing, in addition to the ingredi 50 as well as at Subzero temperatures, in order to overcome ents of the Guth type of propellant, an effective amount the dangers arising from flame-out in commercial air of tantalum, niobium or an alloy of either in divided form liner engines during takeoff or in flight. dispersed in the propellant and embedded in the sur Many flame-propagating materials will rapidly burn, face thereof so that it is readily accessible to our oxidizer. after ignition by the hypergolic igniter system of this in The amount of niobium or tantalum metal or alloy there 55 vention, at a subzero temperature, in the presence of an of in the propellant can be from 0.5 to 10 parts per 100 oxidizer of the system. These materials include all ma parts by weight of propellant. For example, a stream terials which burn at an elevated temperature in an at of oxidizer of this invention, e.g., chlorine trifluoride, is mosphere containing halogen or oxygen and halogen, directed against the exposed surface of a solid propel but which may not ignite spontaneously with a halogen lant containing an alloy of niobium in the combustion 60 fluoride at a subzero temperature. Examples of such chamber of a rocket motor. Upon contact with the combustible materials are hydrogen; ammonia; hydra chlorine trifluoride, hypergolic ignition of the niobium Zines; carbon compounds, particularly alkyl hydrazines, alloy is achieved even at temperatures of about -100 e.g., symmetrical and unsymmetrical dimethyl hydra C. When the combustion of the propellant becomes self Zines, aryl hydrazines, alcohols, mercaptans, ketones, Sustaining, the flow of the oxidizer of our hypergolic igni 65 ethers and hydrocarbons, e.g., acetylene, ethane, propane, tion system can be discontinued. The products of com hexane and kerosenes; carbonaceous materials of all bustion are discharged through the exit orifice of the kinds, e.g., wood, coal, coke, carbon, graphite, cellulosic motor to propel the rocket. fibers, and synthetic polymers; alkali metals, e.g., lithium, In the event that the thrust-providing propellant sys Sodium and potassium; alkaline earth metals, e.g., beryl tem comprises a liquid or powdered fuel in combina 70 lium, magnesium, calcium, strontium and barium; alu tion with a liquid or powdered oxidizer in combusti minum; iron; phosphorus and its lower valence com ble proportions, the hypergolic igniter system of this pounds; Sulfur; boron; silicon; and hydrides and alkyls invention can be used to achieve positive ignition of of the listed chemical elements. After any of these such a propellant system at subzero temperatures. For flame-propagating materials has been ignited at subzero example, an oxidizer useful in the practice of our in 75 temperatures by means of our hypergolic igniter system, 3,213,610 5 6- for example as disclosed in any of the preceding embodi It will be obvious to those skilled in the art that many ments, the oxidizer of our system comprising halogen modifications may be made within the scope of the pres fluoride can be used alone with the above material to ent invention without departing from the scope and spirit maintain a flame and to produce products of combustion thereof, and the invention includes all such modifica tuseful in operation of thrust devices. 5 tions. Table I

Ex- Periodic ample Metal Table Oxidizer Ignition Temperature Results and Comments No. Group . No.

1------Niobium, 4' x 4'x4'---- VA. ClF3, 4 g------Above liquid nitrogen tempera- Violent, incendiary reaction and bright ture, but below M.P. of ClF3. bluish-white flame observed before SE was observed to met, Tube 2------do------WA ClF3, 2 g., ClO3F, 2 g- About (-) 148 F------DuringtSeC. air-warming of tube from liquid nitrogen temperature, white flash of light was observed, followed after a few seconds by bright flame lasting for about 20 seconds. Some 8------do------WA Fluorine, 4 g------No ignition------Liquidfusion fluorine of tube. boiledoffatroom No biobium temperleft. ature. No combustion. Metal gained 4------Tantalum 4'x4'x4'--- WA ClF3, 4 g------Slightly above liquid nitrogen Violent0.0007 g.ignition weight overobserved original as 0.2075g. with temperature. niobium, but earlier. 5------Vanadium, 0.218 g. in fine WA ClF3, 7.6 g.------No ignition------Vigorous bubbling reaction began on granular form. melting of ClF3 and continued until all ClF3 had boiled off while Warming 6------Bismuth, 0.024' wire.------WB ClF3, 6.6 g------do------Liquidto about ClF3 55°F. boiled off at room tem perature. No combustion. Metal gained 0.0002g.over original 0.259.g. 7------Zirconium------IWA ClF3------do------Liquid ClF3 boiled off at room tem 8------Tungsten------WILA ClF3------do------perature.Do. No combustion.

This invention is further illustrated by Examples 1-8 We claim: shown in Table I. In carrying out the demonstration 35 1. An oxidizer-fuel propellant system which is self of our invention as disclosed by the examples, a trans igniting at a subzero temperature when the oxidizer and lucent test tube 34' diameter by 6' long, made of poly fuel are brought in contact with each other said oxidizer chlorotrifluoroethylene was used as a vessel for holding being selected from the group consisting of (a) halogen liquid oxidizer. The test tube was suspended in and fluoride and (b) a mixture of halogen fluoride with at cooled in a liquid nitrogen bath (-196° C.). A Small 40 least one member of the group consisting of fluorine and piece of metal was placed in the test tube and cooled to perchloryl fluoride, said mixture containing at least 4% the temperature of the bath. Oxidizer was then quickly by weight of halogen fluoride; said fuel consisting of (a) condensed into the chilled test tube, the oxidizer cover from about 0.5 to about 10 parts by weight of a divided ing the chilled metal test piece and freezing instantly to form of metal selected from the group consisting essen the temperature of the bath. The liquid nitrogen bath tially of niobium, tantalum, an alloy of niobium with was then removed and the tube allowed to stand at room 45 tantalum, an alloy consisting substantially of niobium, temperature. The contents of the test tube were ob and an alloy consisting substantially of tantalum in com served as the oxidizer warmed. All test work was con bination with (b) 100 parts by weight of other material ducted behind safety glass barricades in a vented hood. combustible in said oxidizer. The results, as shown in Table I, show that, of the 2. The propellant according to claim 1 in which the metals tested, only niobium and tantalum ignite in chlo 50 metal is niobium. rine trifluoride at subzero temperatures. The results also 3. The propellant according to claim 1 in which the show that fluorine does not ignite niobium in the absence metal is tantalum. of chlorine trifluoride even at room temperatures. Fur 4. The propellant according to claim 1 in which the ther, the results show that neither a Group IVA nor a oxidizer is chlorine trifluoride. Group VIA metal nor a Group VB non-metal element 55 5. A method for initiating rocket propulsion at a sub ignites even at room temperature in chlorine trifluoride. Zero temperature which method comprises (a) bringing Also, the results show that a chlorine trichloride-per together separately and substantially simultaneously into chlory fluoride oxidizer mixture ignites below the freez the combustion chamber of a rocket motor a hypergolic ing point of chlorine trifluoride (F.P. -83.5° C.). The igniter system comprising an oxidizer selected from the results, taken in view of the known art, accordingly amply 60 group consisting of halogen fluoride and a mixture of demonstrate the unobvious and unexpected ignition prop halogen fluoride with at least one member of the group erties of the hypergolic igniter system of the invention. consisting of fluorine and perchlory fluoride, said mix Although the practice of the invention has been de ture containing at least about 4% by weight of halogen scribed principally in connection with its use in rocket fluoride, and a fuel comprising a metal selected from the engines at subzero temperatures, the invention can also 65 group consisting essentially of niobium, tantalum and be practiced at above zero temperatures wherever it is their alloys with each other and at least one other metal, desired to obtain positive ignition of a combustible ma thereby causing spontaneous ignition of said metal in said terial, using the hypergolic igniter system of this inven oxidizer; (b) substantially simultaneously providing in tion to ensure such ignition. Thus, our hypergolic ig said combustion chamber a propellant mixture consisting niter system can be used in chemical cutting tools or de 70 of other fuel and oxidizer therefor in combustible propor vices such as those described in Sweetman, U.S. 2,918,125 tions; (c) mixing the combustion products of said hyper and Gall, above, by using the niobium or tantalum metal golic igniter system with said propellant mixture in the or their alloys of our igniter system in combination with combustion chamber, thereby causing ignition of said the halogen fluoride of Sweetman or the halogen-per propellant mixture; and (d) discharging the gaseous re chloryl fluoride mixture of Gall. 75 action products through the exit orifice of said motor. 3,213,610 7 8 6. A method according to claim 5 in which the metal 11. The method according to claim 9 in which the is niobium. metal is tantalum. 7. A method according to claim 5 in which the metal 12. The method according to claim 9 in which the is tantalum. oxidizer is chlorine trifluoride. 8. A method according to claim 5 in which the oxidizer is chlorine trifluoride. 5 References Cited by the Examiner 9. A method for starting a fire at a subzero temperature UNITED STATES PATENTS by auto-ignition which method comprises bringing to gether separately and substantially simultaneously an 2,974,484 3/61 Cooley ------60-35.4 X oxidizer comprising halogen fluoride and a fuel compris 10 OTHER REFERENCES ing at least 0.5 part per 100 parts of fuel of a divided Rosenberg et al., Ind. & Eng. Chem., vol. 45, No. 10, form of a metal selected from the group consisting essen pp. 2283-86, October 1953. tially of niobium, tantalum and their alloys with each Lang, Handbook of Chemistry, 1946, pp. 58-9. other and with at least one other metal, thereby causing a fire by spontaneous ignition of said metal in said oxidizer. 15 CARLD. QUARFORTH, Primary Examiner. 10. The method according to claim 9 in which the metal is niobium. LEON D. ROSDOL., Examiner.